1. Field
The present invention is directed to pyrometallurgical recovery of copper from copper-bearing slags produced in the smelting and refining of copper ores.
2. State of the Art
The extraction of copper from copper ores by pyrometallurgical methods is a very old art, and the losses of copper in slags produced in pyrometallurgical extraction methods has been extensively investigated. It has generally been recognized that copper losses in slags result from copper values dissolved in the slag as well as from copper values mechanically entrained in the slag. Of the total losses of copper in slags, it has been reported that over 70% result from copper values dissolved in the slag, with the remaining losses resulting from metallic copper or copper matte mechanically entrained or suspended in the slag. Mechanically entrained or suspended copper appears in slag as globules in the size range of from about 5 to 100 microns, and for all practical purposes, these globules will not settle out.
A process is disclosed in U.S. Pat. No. 3,682,623 for recovering copper, as black copper, from slags containing copper values. The copper-bearing slags are mixed in the molten state with metallic iron and the melt is subjected to a high degree of agitation, thereby selectively reducing combined copper in the slag to elemental copper. The agitation is produced by rotation of the furnace containing the melt. The metallic copper, e.g. black copper, is then separated from the slag phase.
Copper losses in slags and proposed methods of recovering the copper values from such slags are discussed in an article entitled "The Cleaning of Slags in a Tubular Rotary Furnace", published in Tsvetnye Metally 36(9) date 1963. The authors suggest that, in conventional furnaces wherein a high degree of agitation of the molten contents is not obtained, the interaction between the matte phase and slag phase proceeds at slow rates, being restricted by diffusion of reactants to the interface between the two phases. It was found that intimate mixing of the matte and slag phases improved diffusion of reactants between the phases and accelerated the process of matte drop coagulation. Reverberatory copper slag containing 0.35% copper was treated with sulfidizing agent in a rotary furnace rotating at 5 rpm. After two hours, the molten mass was discharged from the furnace, and the matte and slag phases separated. The slag phase was found to contain 0.1% copper when CaS in an amount of 10% by weight of the slag was used as the sulfidizing agent, and 0.11% copper when FeS.sub.2 in an amount of 15% by weight of the slag was used as the sulfidizing agent.
Processes for pyrometallugically refining copper mattes using a rotary reactor are disclosed in various U.S. Pat. Nos. 3,615,361; 3,615,362; and Re 27,548.